High frequency loudspeakers



Oct. 23, 1962 E. MATsuOKA HIGH FREQUENCY LOUDSPEAKERS 5 Sheets-Sheet lFiled July 27, 1959 INVENTOR z2/Ez. M4 7151/0/64 www M ATTORNEY Oct. 23,1962 E. MATsUoKA 3,059,720

HIGH FREQUENCY LOUDSPEAKERS Filed July 27, 1959 5 sheets-sheet 2INVENTOR 4a MAnsuo/A BYlZ/wn ATTORNEY Oct. 23, 1962 E. MATsUoKA3,059,720

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ATTORNEY Oct. 23, 1962 E. MAT'sUoKA HIGH FREQUENCY LOUDSPEAKERS 5Sheets-Sheet 4 Filed July 27, 1959 INVENTOR /144 raz/0K4 ATTORNEY Oct.23, 1962 E. MATsUoKA HIGH FREQUENCY LoUnsPEAKERs 5 Sheets-Sheet 5 FiledJuly 27, 1959 INVENTOR 54a Mwnsuofm 8% /On/I/ ATTORNEY Patented Oct. 23,1962 3,059,72 HIGH FREQUENCY LOUDSPEAKERS Earl Matsuoka, Thornwood, N.Y., assigner, lby mesneassignments, to Ling-Temeo-Vought, Inc., Dallas,Tex., a corporation of Delaware Filed July 27, 1959, Ser. No. 829,659 14Claims. (Cl. 181-31) This invention relates to loudspeakers, and moreparticularly to a dynamic speaker having a relatively ksmall diaphragm,a conoidal taperedcavity over thediaphragm, and a miniature baille.

The primary object of the invention is the provision of an improveddynamic tweeter loudspeaker havingan extremely high frequency range,such as fifteen to twenty thousand cycles per second, and Wide ,angulardispersion.

-In loudspeakers having such a frequency range constructed according tothe prior art, it has beennecessary to utilize special means such asultra-thin diaphragms actuated electrostatically by the use of a highelectric potential, or the like. `Horn-type tweeters have beenconstructed which have a ran-ge to approximately 14,000 cycles, but thenecessity for transmitting sound from the diaphragm through theinterstices of ahorn throat has so far precluded transmission to theneck of ka horn of frequencies between 14,000 and 20,000 cycles withoutsevere attentuation.

It is the object of this invention to provide a tweeter utilizingpractical commercial diaphragms and a standard dynamic magnetic system,and having a mechanofacoustic coupler adapted to be economically diecast or molded in one piece complete with a diaphragm seat, a taperedcavity, and a miniature central bale.

The term mediano-acoustic coupler `is used to describe the centralelement of the speaker. This term will be found in the text-book byBe-ranek, Acoustics, McGraw Hill Book Co., Inc., New York, 1954, page75, where the author describes a mec-hanceacoustic transducer.

It is another object of the invention to control the extreme highfrequency range of the tweeter, for instance 10 to 20` kilocycles persecond, by the shape of the central baille and suitable mechanicaldamping means.

Another object is to `provide means for centering the diaphragm drivin-gcoil in the magnetic air gap as an integral part of themechano-.acoustic coupler.

Another object is to provide an outer casing which will support andprotect the tweeter without impairing the high frequency performance.

Other objects and features of the invention will appear when thefol-lowing description is considered in connection with the annexeddrawings, in which:

iFIG. 1 is a perspective view kof a loudspeaker constructed according tothis invention;

FIG. 2 is an exploded view of the loudspeaker, showing the tweeter unit,the outer casing, the front `grille, sound absorbent padding, andrelated parts;

FIG. 3 is an enlarged sectional viewtaken on the line 3-3 of FIG. l;

FIG. 4 is a sectional View taken on the line 4-4 of FIG. 3;

FIG. 5 is kan enlarged sectional view of the tweeter unit taken on theline 5-5 of FIG. 4, in which the front is turned toward the right,showing the mechanoacoustic coupler with a miniature central baffle` ofspherical shape, a mechanical damping pad, and'other details;

FIG. 6 is a front elevational view of the loudspeaker of FIG. l with thefront grille removed, showing the front of the tweeter and the soundabsorbent padding;

FIG. 7 is an enlarged front elevatianal .view of the vmechano-.acousticcoupler shown in FIG. 5;

FIG. k8 is a similarly enlarged rear elevational view of themechanoeacoustic coupler shown in FIGS. 5 ,and 7;

FIG. 9 is a sectional view, taken on line '9-9 of FIG. 7, of themechano-acoustic coupler shown in FIGS. 5, 7, and 8, in which the frontis turned toward the 5left,;show ing Vone embodiment of a miniaturecentral baille .adapted to receive a damping pad;

FIG. 10 is a greatly enlar-ged partial `sectional view of the tweetershown in FIG. 5, showing a :port-ion'of the diaphragm andmechano-acoustic coupler;

FIG. 11 is an enlarged sectional view of ane-minoriliment of a tweeteralternative to :that of FIG. .5, `havin'ga miniature central baille ofoblate spherical eshape, `a mechanical damping pad, and other details;

FIG. 12 is a 4great-1y enlarged sectionalview of a portion of thediaphragm of Aa tweeter of the type shown in FIG. 5, showing anotherembodiment of miniature central baille which lits closely to thediaphragm and is not adapted to receive a damping pad; .and

FIG. 1'3 is a chartshowing illustrative .frequency characteristics oftweeters constructed according to vthe two principal embodiments of thisinvention.

Referring to FIGS. 1 to 6, the high frequency loudspeaker, generallyindicated by the reference lnumeral 25, constructed according to thisinvention comprises an outer rear housing 26, a front grille 27, and a.-hgh frequency or tweeter unit 50` mounted therebetween. The rearhousing is preferably a oneepiece plastic molding, having thereonsuitable projections, such fas 410),. for support and having thereinsuitable means such vas the cylindrical portion 37 and its supportingrib 38 Vfor supporting the tweeter unit 50. Thegrille 27 is fttedfoverthe front and the ends 39 thereof folded around the end portions 34 ofthe housing. A lip 41 extends along the top and bottom edges of thehousing to receive the top and -bottom edges of the grille. There ispreferably a protru-sion 28 in the middle of the grille `2,'7 for .thepurpose of allowing the tweeter to be mounted well forward in thehousing with the front edge V67 disposed flush with the front edge 42 ofthe housing and disposed forward thereof. -If this is not done, it hasbeen found experimentally that the Iresponse becomes irregular at highfrequencies due to diffraction of sound around the edge 42 of thehousing. It has also been found that the face of the housing, i.e., thegril-le around the redge 67 of the tweeter unit 50, is preferably madeperforated, as by using porous material for the grille 27, otherwise thehigh vfrequency response is irregular. It has furthermore been foundthat the interior of the housing is preferably substantially filled withsound absorbent padding whicheliminates the standing waves therein. Thepads 29 and 30 illustrate a preferred form of such padding, and haveportions 31 and 32 .cut away to provide clearance for .the various partswhich .occupy lthe housing. One of these may be the capacitor 3:3, whichis mounted by the bracket 34. The tweeter kterminals 315 and 36 areshown protruding .through the inside of the housing in FIG. 2.

Referring to FIGS. 5 to 10, the tweeter unit, generally indicated by thereference numeral 50, is .comprised'ofa diaphragm 44 driven by a voicecoil 58, a magnetic system for establishing magnetic llux in the argap60, `and .the acoustic .coupler 70. The magnetic system is vcomprised of.the pole ypiece 61, the pole plate =62, .the

ring-shaped magnet 63, the pole plate 64, and vthe nonmagnetic centeringannulus 65. It is preferable to utilize high ilux density of the orderof 10,000 to 13,'O0Ogauss, in order not only to secure high sensitivity`but to establish electro-dynamic damping of transient response. Y

Referring particularly to FIG. l0, the diaphragm 44 has a generallycurved acoustic driving portion 55 as indicated and a generally flatannular supporting llange 56. The diaphragm is connected to the voicecoil by vthe voice coil form 57. The voice coil 58 and form 57 have apredetermined mass, to be subsequently referred toas voice coil mass.Terminals 51 and 52 (see FIG. 2) are provided by lugs aflixed inapertures 85 and 86 (see FIG. 7) of the coupler 70. The flange 56 of thediaphragm is clamped in an assembly of washers 59, the Washer betweenthe flange and 4the rear curface of the coupler 70 having the thickness'77, which is small and of the order of .030 inch.

The front surface 75 of the mechano-acoustic coupler 70 extends from theflange portion 56 of the diaphragm forwardly and outwardly in agenerally conoidal shape, which in the drawings is shown conical. Thecoupler thus has a generally ring shape which is symmetrical about thecentral axis and which has a centrical aperture of predeterineddiameter. In the middle of the mechanoacoustic coupler is a miniatureacoustic baffle, which in the embodiment shown in FIGS. 1 9 is a sphere90 which, in the preferred embodiment7 has the rear portion 96 recessedto receive a damping pad 99. The conical shape of the front surface 75of the coupler 70, taken in conjunction with the shape of the centralbaille 90, acts to provide acoustical radiation resistance loading onthe diaphragm portion 55 by constricting the solid angle into which thediaphragm radiates whereby to greatly improve the efficiency over thatpossible without the coupler, in a manner analogous to the action of ahorn. The mechanical damping of the center of the diaphragm provides amatched mechanical impedance termination for the mechanical transmissionline consisting of successive annular portions of the diaphragm, alongwhich vibrations are propagated from the voice coil forward and inwardtoward Ithe middle of the diaphragm.

Referring now to FIG. 8, it will be seen that the rear surface of themechanic-acoustic coupler 70 has a llat annular portion 81 adapted tofirmly engage the flange 5.6 of the diaphragm. The rear surfaceintermediate between this annular portion and the periphery ispreferably skeletonized with alternate ribs 82 and spaces 84therebetween. The rear surface 83 (see FIG. 9) of the ribs is taperedforwardly in order to avoid pressing on the portions of the washerassembly 59 external to the diaphragm llange clamping portion. See FIG.9.

The outer peripheral portion of the mechano-acoustic coupler 70 ispreferably formed with an annular shoulder 74 having an innercylindrical surface 88 adapted to tit closely over the outer edge of thepole plate 62 for the purpose of axially aligning the coupler with theflange 56 of the diaphragm. Optionally, this surface 88 may be machinedto a close tolerance, the machining operation terminating in theundercut 98 (see FIG. 9). The flange 56 is preferably cemented to therear face 81 of the coupler, in a suitable centering jig as well knownin the art, as one step in assembling this loudspeaker. This shoulder 74then constitutes an economical means for centering the voice coil 58 inthe air gap 60. The rear edge 89 is extended axially beyond the end ofthe voice coil 58 so that the assembly of coupler and diaphragm partscan be rested face upwards without danger of damage to the voice coil.The annular shoulder 80 is vadapted to be engaged by the rim 66 of thecasing 68, which is rolled over the shoulder 80 in a final assemblyoperation.

In the preferred embodiment of this invention, a plum rality of smallprojecting members 97 are provided around the periphery' of the frontedge 67 of the mechanoacoustic coupler for the purpose of preventingdamage to the acoustic baille 90 when the assembly is placed face downupon a flat table. Alternatively, as shown in FIG. l1, the acousticbaille maybe made retracted from the edge as shown by the oblatespheroid 91, and the acoustic performance is only slightly, if any,impaired thereby.

In another embodiment of this invention, the miniature acoustic baillemay take the general form of a hemisphere 92, as indicated in FIG. l2,with the rear side thereof conformant to the shape of the middle of thediaphragm 55 fand adapted `to be disposed in closely spaced relationshipthereto.

The miniature baille is retained, in each embodiment of this invention,by at least one rib 95 aflixed to the edge of the coupler 70. Other ribsmay be utilized if desired, but the aggregate section inserted therebyinto the path of sound transmitted outwards from the diaphragm should bea small percentage of the total area between the conical surface 75 andthe miniature ballles 90, 91, and 92.

In a preferred embodiment the acoustic baille 90 has a diameter betweenone-half and three-quarters of that of the voice coil 57.

The acoustic performance is dependent upon the masses of the voice coil58 and the .driving portion 55 of the diaphragm, the stiffness andpropagation coefficients of the diaphragm 44 and the air chamber beneaththe diaphragm, the angle 76 and height 87 of the conoidal portion of thecoupler and the proportions of the central miniature acoustical baille90. The mass of the voice coil 58 is preferably half of that of thedriving portion 55 of the diaphragm, which for a voice coil having adiameter of three-quarter inch is of the order of .075 gram, voice coilmass.

In one embodiment of this invention, the voice coil is three-quarters ofan inch in diameter; the diaphragm driving portion 55 has substantiallyuniform thickness between .002 and .003 inch with the middle no thickerthan the edge; and the flange portion 56 is approximately .001 inchthicker than the driving portion 55. The preferred material isphenolic-impregnated fabric. In the preferred embodiment of thisinvention, the driving portion is convex, which is intrinsically bestsuited to radiating sound over a complete hemisphere.

As a preferred embodiment of this invention, the mean included angle 76of the conical frustum portion is between 80 and 120 degrees.

It is essential to provide an acoustic chamber 43 behind the diaphragm.In general the proportions of this are preferably as indicated in FIG.5, in which the chamber is bounded on the rear by the pole piece 61 andon the front by the diaphragm portion 55.

There is preferably a minute overhang of the inner edge of the acousticcoupler 70 over the diaphragm flange having the dimension 78. See FIG.l0. As this dimension is increased from zero to the width of the ange,the acoustic resistance loading on the diaphragm is increased, resultingin increased efficiency in the 3000 to 16,000 cycles per secondfrequency band, whereas the frequency range may be reduced from 23,000to 16,000 cycles by this increase in the overhang 69.

Illustrative frequency characteristics taken with tweeters utilizing thevarious embodiments of this invention are shown in FIG. 13. All curveswere taken with a capacitor having 4 microfarads in series With thetweeter unit, the impedance of the unit being of the order of ten ohms,whereby the series combination is adapted to be connected in parallel toa standard lowand mid-range loudspeaker having an impedance ofapproximately l0 ohms, without any other electrical networks fordividing the frequency ranges or the like.

The solid line is an untouched reproduction of a laboratory curve takenwith a substantially llat microphone, on the tweeter unit utilizing asubstantially spherical central baille as shown in FIGS. 5 to 10, andwithout the outer housing of FIGS. 1 4. It may be seen that the responseis substantially flat from 3000 to above 20,000 cycles per second. Thestructure of FIG. ll has substantially similar characteristics. This isobviously greater than the frequency range of any previouselectro-dynamic tweeter and extends well beyond the limits ofaudibility. It is more linear and free from background noise thancorona-type tweeters and has, in contrast to such speakers, anindefinitely longlife.V It is smaller and more rugged than electrostaticspeakers and has none of the disadvantages of that type.

The dashed line of FIG. 13 shows the relative response using thealternative form of miniature baille shown in FIG. 12. It may vbe seenthat vthe output is somewhat greater up to 15,000 cycles than ischaracteristic of the spherical baille as shown in the solid curve, buta cutoil occurs there. This is .an advantage in applications where thesignal-to-noise ratio in a given audio channel drops sharply at thisfrequency, although where the channel is not subject to such alimitation the solid curve is preferable.

The response as shown in the solid curve is 2 to 5 db more sensitive,the greater increase occurring at extreme high frequencies, than thatfor the hypothetical case wherein the angle 76 of the front of thecoupler is increased to the order of magnitude o-f k180 degrees andwherein the miniature baille .is indeilnitely reduced in size.Furthermore, the solid curve is much smoother than thatin thehypothetical case, which is partially attributable to the use of thedamping Vpad 99. When the latter is omitted, the reponse is generallymore ragged, especially between 15,00 and 20,000 cycles.

The frequency response of the tweeter assembled in the housing, as shownin FIGS. l to 4, is at least as ilat as that shown in the solidcurve ofFIG. 13, the slight rise at the extreme high frequency end beingcompensated by the action of the grille. The polar characteristics ofthe resultant tweeter may be described as being substantially uniformover a solid angle of 180 degrees up to 10,000 cycles, above whichfrequency the response is somewhat more restricted. At 15,000 cycles,for instance, the response is 8 db reduced at an angle of 30 degreesfrom the central axis. l

The invention has been .described as embodied in a loudspeaker, thoughit is to be understood that the same construction is usable as a soundpickup device.

The drawings and description are to be taken generally as illustrativerather than restrictive on the broad invention. Various changes may bemade in manufacture, such as diilerent locations of the casting partingsurfaces, and the like.

In the claims the term transducer isused to indicate a sound-translatingdevice, usable either as loudspeaker or microphone.

It will be obvious to those skilled in the art that various changes maybe made in the invention without departing from the spirit and scopethereof, andtherefore the invention is not limited by that which isrshown in the drawing and described in the specification, but only asindicated in the appended-claims.

I claim:

l. ln la transducer of-the type described, a tweeter unit comprising: adiaphragm with a domed-shaped acoustic driving portion, symmetricalabout a central axis, said diaphragm having an annular rim; and a voicecoil concentric therewith having a preselected diameter; a magneticsystem having a concentric air gap for surrounding the voice coil; amechano-acoustic coupler having a generally ring shape symmetrical aboutsaid central axis, the front thereof having a generally conoidal frustumshape with a predetermined included angle, said front disposedconcentrieally with the axis of the diaphragm, and having a centralopening therein, a generally planar rear surface juxtaposed to theannular rim of the diaphragm and acoustically sealed thereto; saiddome-shaped driving portion being convex with respect to said couplerand extending into said opening, an exterior annular peripherallydisposed shoulder on said coupler concentric with Said conoidal portion;miniature baille means adjacent to the center of the convex dome portionof said diaphragm in spaced relationship thereto and having a diametersmaller than that of the voice coil; means for supporting said baillemeans on said coupler comprising at least one r6 rib; and a casingsurrounding the magnetic system and diaphragm and ailixed to'saidannular shoulder.

2. In a transducer as described in claim 1, -characterized by the frontsurface of said conoidal frustum portion having a mean included anglebetween and 120 degrees.

3. In a transducer as Adescribed in claim 1,means for damping resonantvibrations of the center of the diaphragm comprising a damping padinterposed between the front of the diaphragm and the rear of theminiature baille means.

4. A tweeter unit and cabinet combination comprising a tweeter unit asdescribed in claim l, a rectangular cabinet having an open face coveredby an open-.mesh grille, an outwardly domed portion in the middle of thegrille, means for supporting the tweeter unit juxtaposed to the innerside of said domed portion and sound absorbent padding substantiallyillling the cabinet around the tweeter.

5. In a tweeter unit as described in claim 1, saiddiaphragm having athickness at the center substantially equal Ato and no greater than thatat the edge thereof.

6. In a tweeter unit as described in claim 1, wherein compliant airvcushioning means are coupled to the rear of said diaphragm comprising achamber bounded in part by the rear surface thereof and having a meanthickness of at least one-quarter of the diameter of the voice coil.

7. A mechano-acoustic coupler having a generally ring shape portionsymmetrical about a central axis and having a central aperture ofpredetermined diameter, a front surface having the shape of the frustumof a conoid and a rear surface having a centrally disposed ilat annularportion; baille means disposed in centrally spaced relationship to thefront surface of the coupler having a mean diameter smaller than that ofthe central aperture and lying within the confines of said frontsurface, at least one rib `connecting the baille means with the ringshape portion, the ring shape yportion and the baille means forming anacoustic coupler for a ilanged diaphragm aillxed by its ilange to therear flat annular portion; the rear surface of the ring shape portionhaving a peripheral rearwardly-extending ilange with an interiorcylindrical surface concentric with the central axis for aligning thecoupler with a magnetic system.

8. A mechano-acoustic coupler having a generally ring shape portionsymmetrical about a central axis and having a central aperture ofpredetermined diameter, a front surface having the shape of the frustumof Va conoid and a rear surface having a centrally disposed ilat annularportion; baille means disposed in centrally spaced relationship to thefront surface of the coupler having a mean diameter smaller than that ofthe central aperture and lying within the conilnes of said frontsurface, at least one rib connecting the centrally disposed member withthe ring shape portion, the ring shape portion and the central memberforming an acoustic coupler for a ilanged diaphragm ailxed by its ilangeto the rear flat annular portion, the rear surface of the ring shapeportion having a peripheral rearwardly-extending ilange with an interiorcylindrical surface concentric with the central axis for aligning thecoupler with a magnetic system, and a peripherally disposed annularshoulder on the front surface of the ring shape portion concentric withthe central axis for mating with the rim of a casing.

9. A mechano-acoustic coupler as described in claim 8 consisting of oneintegral die-formed piece.

10. A mechano-acoustic coupler having a generally ring shape portionsymmetrical about a central axis and having a central aperture ofpredetermined diameter, a front surface having the shape of the frustumof a conoid and a rear surface having a centrally disposed ilat annularportion; a spheroidal baille member disposed in centrally spacedrelationship to the front surface of the coupler having a mean diameterin the plane perpendicular to the central axis smaller than that of thecentral aperture and lying within the confines of said front surface,the spheroidal member having at least one rib connecting the spheroidalmember with the ring shape portion, the ring shape portion and thecentral member forming an acoustic coupler for a flanged diaphragmaffixed by its flange to the rear flat annular portion.

11. In a transducer of the type described, a tweeter unit comprising: adiaphragm with a generally curved acoustic driving portion, symmetricalabout a central axis, said diaphragm having a front and rear surface andhaying a thickness at the center substantially equal to and no greaterthan that at the edge thereof; a generally flat, annular rim; and avoice coil concentric therewith having a preselected diameter; amagnetic system having a concentric air gap for surrounding the voicecoil, the central pole having a flat front surface; compliant aircushioning means coupled to the rear of said diaphragm comprising achamber bounded by the rear surface thereof and by the flat surface ofthe magnetic pole; a mechano-acoustic coupler having a generally ringshape symmetrical about said central axis, the front thereof having agenerally conoidal frustum shape with a predetermined included angle,said front disposed concentrically with the axis of the diaphragm, agenerally planar rear surface juxtaposed to the annular rim of thediaphragm and acoustically sealed thereto: an exterior annularperipherally disposed shoulder on said coupler arranged concentric withsaid conoidal portion; miniature baille means in juxtaposition to thecenter of the diaphragm in spaced relationship thereto and having adiameter less than that of the voice coil; means for supporting saidbaffle means on said coupler comprising at least one rib; and a casingsurrounding the magnetic system and diaphragm and aflixed to saidannular shoulder.

12. In a transducer of the type described, a tweeter unit comprising: adiaphragm with a generally curved convex acoustic driving portion,symmetrical about a central axis, said diaphragm having a flange with aperipheral flat annular rim; a voice coil concentric therewith having apreselected diameter; a magnetic system having a concentric air gap forsurrounding the voice coil; a mechano-acoustic coupler having agenerally ring shape symmetrical about said central axis, the frontsurface thereof having a generally conoidal frustum shape with apredetermined included angle and disposed concentrically with the axisof the diaphragm, the rear surface thereof having a first flat annularshoulder for sealing to the flat annular rim of the diaphragm and asecond generally flat annular shoulder offset forwardly from the firstand overhanging the flange of the diaphragm; and miniature baffle meansadjacent to the center of the convex portion of the diaphragm in spacedrelationship thereto and having a diameter smaller than that of thevoice coil.

13. A tweeter comprised of a generally ring-shaped member having acentral axis, the inner surface having the shape of an inverted conoidalfrustum that has an included angle of between and 120 degrees andsymmetrical about said central axis, an end on the ringshaped member,said end having a planar annular surface perpendicular to the saidcentral axis, a diaphragm having a convex domed portion and a generallyflat flange portion, means for aflixing part of said flange portion tothe planar annular surface, the diaphragm dome portion having athickness at the middle no greater than that at the edge of the dome, avoice coil suspended from the edge of the dome on the concave sidethereof, and a baille-like member suspended in the middle of saidringshaped member having a diameter between one-half and three quartersthat of the diameter of said voice coil and disposed in closely spacedrelationship to the convex side of the dome, whereby the combination ofthe conoidal frustum and the baille-like member comprise a horn-likemechano-acoustic coupler having a miniature acoustic baffle in themiddle thereof, whereby to provide acoustical radiation at extreme highfrequencies over a wide angle. 14. A tweeter and cabinet assemblycomprising, in combination a tweeter characterized by mechano-acousticcoupling means comprised of a generally ring-shaped member having acentral axis, the inner surface having the shape of an inverted conoidalfrustum having an included angle between 80 and 120 degrees andsymmetrical about the central axis, a diaphragm having a convex domedportion and a generally flat flange portion, means for supporting saidflange portion adjacent a planar annular surface on said ring-shapedmember, the diaphragm dome portion having a thickness at the middle nogreater than that at the edge of the dome, a voice suspended from theedge of the dome, and a baille-like member suspended in the middle ofthe ring-shaped member having a diameter between one-half andthree-quarters that of the domed portion and disposed in closely spacedrelationship thereto, whereby to provide acoustical radiation at extremehigh frequencies over a wide angle; a cabinet having a perforated frontwall and solid rear wall and a top having a frontal edge; said tweeterbeing affixed to said cabinet with the front surface of said tweeterdisposed substantially in a plane perpendicular to the central axis ofthe tweeter and intersecting the frontal edge of the top wall; and soundabsorbent padding mounted in the cabinet around the tweeter.

References Cited in the file of this patent UNITED STATES PATENTS1,907,723 Bostwick May 9, 1933 1,964,606 Thuras June 26, 1934 2,475,782Giannini July 12, 1949 2,926,740 Holland Mar. 1, 1961 FOREIGN PATENTS494,696 Great Britain Oct. 31, 1938

